Function pm#from/to_place__from/toplace (pm#process -> pm#spatial_object)
  supertype:  pm#from/to  pm#relation_from_process_only
  subtype:  pm#from_place (pm#process -> pm#spatial_object)
  subtype:  pm#to_place__destination (pm#process -> pm#spatial_object)
  subtype:  pm#via_place__viaplace__via (pm#process -> pm#spatial_object)
  subtype:  pm#path (pm#process -> pm#spatial_object)